Recently, it has been realized that bodies for aircrafts or automobiles or their structural parts are formed from fiber reinforced plastic (FRP) to reduce the weight of bodies. Various kinds of FRP have been proposed such as thermosetting plastic including carbon fibers as reinforcing fibers (CFRP), thermosetting plastic including glass fibers as reinforcing fibers (GFRP) or thermosetting plastics including, as reinforcing fibers, heat resistant synthetic resin fibers such as aromatic polyamide, aromatic polysulfone, aromatic polyimide etc. Usually, a laminated member is formed with a plurality of resin layers with the reinforcing fibers alternately arranged in an oblique or an oblique cross fashion (see Reference Patent Document No. 1). Reference Patent Document No. 1: Japanese Laid-open Patent Publication No. 126557/2005.
In using FRP members as structural elements for bodies of aircrafts or automobiles, it is usually required to form apertures, by drilling, for passing fasteners, such as bolts etc., and connecting the structural elements. The apertures in FRP members (e.g. an FRP member and laminated member including therein carbon fibers, glass fibers etc.) are formed using a general drilling apparatus, constructed so that a drilling tool is simply rotated by a driving spindle. The drilled surface of the aperture, formed by such a general drilling apparatus, is rough. This is due to heat generated by frictional resistance during the drilling process. Additionally, the life of the drilling tool of such as a drill is extremely shortened.
It is supposed that the irregular deformation in the surface of a drilled aperture is caused by an excessive generation of heat in the cutting edges of the drilling tool. This is caused by the drilled surface of FRP members where the reinforcing fibers (e.g. carbon fibers, glass fibers etc.) are arranged in the same direction as the cutting direction of the drilling tool in the general drilling apparatus. In addition, it is also supposed that the life of the drilling tool would be shortened by the excessive heat giving rise to adverse effects on its cutting edges.